Future-proofing fisheries: is increasing sea temperature altering commercial decapod crustacean catch in the bailiwick of jersey?

Global sea surface temperature (SST) has risen ~0.13°C per decade over the 20th century. Ocean warming is strongest in the north-east Atlantic around the UK where SST is increasing approximately six times faster than the global average. Particularly prone to this warming is the Bailiwick of Jersey where heat retention is facilitated by gyres formed as water enters the Bay of Granville. SST across Jersey has increased from 12.2°C (1946 to 1965) to 13°C (1988 to 2007). This increase is concerning for commercial species as temperature influences migration, growth, and breeding, in-turn impacting catchability. Commercial fishing in Jersey is economically dominated by shellfish, with lobster (Homarus gammarus) and crab (e.g., Cancer pagurus, Maja brachydactyla) constituting ~70% of landings financially. Despite fisheries management, annual landed weight of C. pagurus and H. gammarus has been undergoing decline. This study investigates Jersey’s sea temperature in conjunction with commercial decapod crustacean fisheries, focusing on Cancer pagurus, Maja brachydactyla, and Homarus gammarus, representing catch by Landings per Unit Effort (LPUE). Temperature loggers were placed throughout the region recording sea-bed temperature from 2020 to 2022. Sea temperature interactions were established by comparing logger data to Jersey met office SST and no significant difference was found. This was attributed to the lack of thermocline in Jersey waters and allowed for the use of SST as a proxy for regional sea temperature. In this context, generalised additive models analysed LPUE interactions with temperature. Whilst C. pagurus LPUE generally declined, H. gammarus LPUE increased with temperature. However, catch was found to decrease for both C. pagurus and H. gammarus after 18°C, suggesting thermal limits for the fishery. Conversely, LPUE of M. brachydactyla increased with temperature, suggesting temperature change may have differential effects on shellfish fishery productivity. Whilst temperature cannot be determined as the sole factor causing current declines in LPUE, this study suggests future ocean warming may impact catchability and the value of Jersey’s shellfish stocks. Therefore, suggestions are made concerning fisheries management and horizon scanning to future-proof Jersey’s fisheries in the face of climate change.